FIELD OF THE INVENTION
This invention relates to a sensor system in a printhead scanner and more particularly to a sensor and encoding scheme for reading printhead position along a scan line to provide low cost print registration that is both contamination and ambient light resistant.
A recurring problem for printers, copiers, and other related machines employing a printhead that scans across media to be imprinted is the accurate registration of the printhead, on a pixel to pixel basis, during printing. Often this is accomplished by an optical sensor mechanically coupled to the print carriage. As the printhead moves across media to be imprinted, a sensor beam is alternatively interrupted and transmitted by either a rotary or lineally disposed occluding means. A detector, commonly a phototransistor, receives the sensor beam and an alternating voltage pattern is formed by suitable amplification of the induced photocurrent which is then passed through a resistor. It is important that the alternating voltage pattern be triggered properly so that the printhead will print pixels which are aligned correctly.